It appears to be Schist and/or Gneiss conglomerate with Sandstone and other compositions compressed together and it is probably loaded with little Rubies, Sapphires and/or Garnets. No real value other than placing them where sunlight can hit them and watch the displays of sparkles, reflection and refractions in the sunlight. If I had to guess, I would imagine the rock weighs almost 3 times what a similar sized and shaped sedimentary rock weighs!
Frank